Relatively Mild Start For 2013

Despite the relatively frequent cold snaps that punctuated January 2013, the month ended up generally on the slightly milder than average side, preliminary data shows. In the Greater Grand Forks area the monthly average temperature at the UND/NWS Climate Station of 8.5F was 1.1 degrees Fahrenheit above the long term average. At the Grand Forks Airport the 31 day average temperature was 8.8F, which was a departure from normal of 2.1 degrees Fahrenheit. In the southern Valley at Hector Field in Fargo the average temperature was 10.8F, or 1.5 degrees Fahrenheit above the 1981-2010 normal. Not only was it milder than normal at these locations, the entire Red River Valley generally experienced a slightly milder than normal start to 2013. This comes as a surprise to some, as in just the last few days of the month some pretty cold air invaded the northern plains.

Zooming in to the local level one can see there was some variability over the states of North Dakota and Minnesota. Based on preliminary data from NWS Cooperative Observers and Automated Weather Observation Stations, just about all of the regular reporting points had temperatures above the 30 year normal; a few locations were close to or just a tad cooler than average.

Image provided by the High Plains Regional Climate Center in Lincoln NE

Image provided by the High Plains Regional Climate Center in Lincoln NE

Precipitation exhibited the usual significant variability from one location to the next. The late January snowstorm brought the monthly totals to above the long term average from the far Southern Red River Valley into north central Minnesota, while the majority of eastern North Dakota and the Devils Lake Basin experienced below median precipitation.

Image provided by the High Plains Regional Climate Center in Lincoln NE

Image provided by the High Plains Regional Climate Center in Lincoln NE

So why was the climate so variable across the region the past month? The Jet Stream, that river of fast moving air high in the atmosphere was in a "Split Flow" configuration much of the month, with one branch of the Jet flowing from Mexico across Texas up into the northeastern US, while a weaker branch entered the northwestern U.S. and northwestern Canada. This northern branch brought occasional Arctic air south while also pushing milder Pacific air into the region. The southern stream of the Jet, while generally remaining well to the south did move far enough north to produce the heavy snows. Below is an image that illustrates the average position of the Jet Stream during January 2013. The southeastern US on into the northeast experienced the highest precipitation totals, as is common closer to the stronger jet core.

So why was the Jet Stream "split" and the southern branch stronger?The white lines & arrows [in the image above] represent the flow of air in the "upper layer" of the atmosphere, around 35,000 feet above sea level. Below is an image that illustrates the average upper air pattern during January 2013. A large ridge of higher pressure over the eastern U.S., combined with lower pressures to the north helped increase the winds aloft. An unusually active Pacific Tropical pattern regularly fed moisture into the Jet Stream which assisted in the active weather pattern.

The green arrows [in the image above] represent the flow of air in the "middle layer" of the atmosphere, around 20,000 feet above sea level. Note that while North Dakota and Minnesota were mainly in the northern flow, higher pressure over the northeast Pacific helped modify the coldest air-masses coming south from Canada. Further, the general lack of a consistent and deep snow-pack over the region reduced the amount of cooling near the surface as the warmer ground helped in the air-mass modification.What is in store for the rest of the meteorological winter? The updated outlook from the Climate Prediction Center suggests we will see a pattern that continues to bring variable conditions to the northern plains, resulting in an increased risk for above normal precipitation and temperatures ending up close to the climatological median values. We expect to see some fairly wide swings in temperature, as we saw during January. Looking ahead into the March and April time period there is a tendency for slightly cooler temperatures with an enhanced risk for continued above median precipitation.